Revisiting Lorentz-factor constraints in blazars and gamma-ray bursts based on polarization-dependent gamma-gamma absorption

Project Description:

Gamma-ray bursts (GRBs: seconds to minutes long flashes of gamma-rays, probably resulting from either the collapse of a very massive star or from the merger of a neutron star with another neutron star or a black hole) and jetted active galactic nuclei (in particular, blazars) are amongst the brightest sources of high-energy gamma-rays in the Universe. It is well established that the high-energy emission regions in GRBs and blazars are moving with highly relativistic speeds very close to the speed of light, in a direction closely aligned with our line of sight. One of the arguments supporting this is that high-energy gamma-rays observed from these sources would be absorbed by lower-energy target photons in photon-photon absorption, resulting in electron-positron pair production, if the emission region was stationary or moving slowly. Lower limits of the Lorentz factor (and thus, the speed) of the emission region have been derived from calculations / estimates of the gamma-gamma absorption opacity on the observed lower-energy radiation fields that are produced in the same emission region as the gamma-rays. Polarization effects have so far been ignored in such estimates. However, the low-energy radiation in these sources is likely highly polarized synchrotron radiation, while the gamma-rays may also be polarized. In this case, the gamma-gamma absorption opacity may be over-estimated when neglecting its polarization dependence. The goal of this project is to quantify the error incurred when estimating minimum jet Lorentz factors neglecting polarization effects. It will specifically apply the polarization-dependent gamma-gamma absorption formalism of Boettcher (2014: ApJ, 795, 35) to Lorentz-factor estimates in blazars and GRBs.

Research Area:

Astrophysics

Project Level:

Masters

This Project Is Offered At The Following Node(s):

(NWU)